Conventional electrical devices are usually supplied with power in a wired mode. In the wired mode, it is necessary to connect the electrical device and the power supply device via conductive wires, so that the power supply device can supply electricity. Even power transmission in a short distance also needs electric wires and cables to supply electricity. In some cases, supplying power in the wired mode is not convenient. If the electrical device can be supplied with electricity in a wireless mode, the electrical device can be disconnected from the power supply, and thus powering the electrical device will become very convenient.
The wireless energy transmission technology is a process which transmits electricity from electricity transmitter to loads without using conventional electric wires. Currently, the domestic and abroad study mainly focuses on supplying electricity to the electrical device using magnetic coupling resonant wireless power transmission technology. In the magnetic coupling resonant wireless power transmission technology, especially in the process of charging a rechargeable battery, the utilization of electrical energy is a very important parameter.
FIG. 1 illustrates a receiving circuit for wireless power transmission in prior art, which consists of a resonant circuit 7, a full bridge rectifying circuit 8, a LC filtering circuit 9 and a diode D10, wherein the resonant circuit 7 consists of an inductor L6, a capacitor C11 and a capacitor 10, the full bridge rectifying circuit 8 consists of four diodes D6-D9, the LC filtering circuit 9 consists of an inductor L7 and a capacitor C12. The resonant circuit 7, full bridge rectifying circuit 8 and LC filtering circuit 9 of FIG. 1 are known in the art, and thus are not described in detail herein. During the process of charging the rechargeable battery B by the receiving circuit for wireless power transmission in prior art, a resonant transmitting circuit (not shown in FIG. 1) generates an alternating magnetic field, such that the inductor L6 of the resonant circuit 7 has an alternating magnetic field, thereby generating an electromotive force across the two terminals of the capacitor 11. The full bridge rectifying circuit 8 rectifies the electromotive force and outputs a rectified voltage to the LC filtering circuit 9. A DC is obtained at two terminals of the capacitor C12 after filtering, and finally the rechargeable battery B is charged via the diode D10. With the increase of charging time and the energy stored in the rechargeable battery B, the transmission efficiency of electrical energy becomes lower and lower. A lot of electrical energy will be lost as heat at the latter period of charging the rechargeable battery B, thereby reducing the utilization of electrical energy, and resulting in increased temperature of components in the receiving circuit, which may damage the electronic components in the receiving circuit.